We open up in a Civil War battlefield in 1863. Countless dead Union soldiers lay on the ground. Two men, Fredrick Aiken (James McAvoy) and his friend Nicolas Baker (Justin Long) are still alive albeit wounded. There are medics around them looking for survivors. Aiken is telling Baker a joke to keep him lucid until help arrives. Aiken calls for the medics and tells them to take Baker first, even though it looks like he will die. Aiken is a captain and has seniority but Aiken tells them that is an order so they take Baker first.
2 years later.
It is April 14, 1865. Aiken and his friend Baker (who survived his wound to his leg with just a limp) are with another friend, William Hamilton (James Badge Dale) at a party celebrating the end of the war. Baker wants to meet Edwin Stanton (Kevin Kline), who is Lincoln's secretary of war. However, he cannot just go up to him without an introduction. Aiken goes to say hello before he is stopped by Reverdy Johnson (Tom Wilkinson), Aiken's mentor. Johnson distracts Baker and Hamilton presenting them to some women as war heroes. Johnson pulls Aiken aside for a private word as Stanton walks by. Stanton tells the men that President Lincoln will not be attending the party as his wife wanted to go to the theatre instead. Stanton speaks to Aiken, saying he could use a man like him in the War department.
Aiken is met by his wife Sarah (Alexis Bledel) and they sit outside and talk. Sarah is happy that Aiken has come back alive. Though she sees Stanton offer is a nice one, is content to have her husband in civilian clothes, even if he does look good in a uniform.
We see several small groups of men lay in wait in order to set their plan in motion. One man goes to a different party and orders a drink from the bar, waiting for someone. He has a gun in his coat which attempts to conceal. He sees his target, the Vice President. He arouses suspicion by continuously looking over to him, and cannot find his courage. He briskly leaves the party.
Another man enters the house of the Secretary of State William Seward. The man is Lewis Payne (Norman Reedus). His job is get to the Secretary who is ill of health and kill him. Payne has a gun that he tries to use on the guard but it misfires. He then races up to the man and stabs him. He bursts into the room and stabs Seward's wife then stabs Mr. Seward within an inch of death before running off.
The final conspirator John Wilkes Booth, enters Ford Theatre. He moves along the backstage while a play is going on in front of him. He finds the entrance to the box seats where the President is watching the show. He cocks his pistol and fires a single shot into the President's head. He jumps off the balcony into the crowd. Booth jumps on stage saying the South will rise again.
Back at the party, Aiken, Baker, and Hamilton hear that the President has been shot. They rush out to contain order though that is quite difficult. The President is carried to a house nearby in an attempt to treat him but to no avail. By the time Stanton gets there, The President is near death. Stanton orders that General Grant be brought back to D.C. Stanton can hear Mary Lincoln sobbing and though realizing she is mourning orders that she is removed from the room. By the morning, the President is dead, and one of the largest manhunts begins.
A montage shows the next several days. The government manhunt rounds up almost all the conspirators save for John Wilkes Booth and David Herold. Among the accused is Mary Surrat (Robin Wright), mother of John Surrat (Johnny Simmons) who was considered Booth's right hand man.
Union soldiers catch up to Booth and Herold in a barn. Herold gives himself up, but Booth will not. The soldiers set the barn on fire and one of them looks into the barn and fires, killing Booth.
The eight conspirators (not counting John Surrat) are held in separate cells. They will be charged in a military tribunal ordered by Stanton, in order to secure swift guilty verdicts and executions for the public that demands them.
Aiken goes to see Johnson. Johnson has taken the case of Mary Surrat and will defend her in court. Johnson has the deck stacked against him though; Stanton has filled the tribunal with loyal judges and with the public clamoring for blood, they will do everything they can to assure that the words "Not Guilty" are never heard in that courtroom. He wants Aiken to be his second chair. Aiken is flabbergasted that Johnson would defend a southerner that is clearly guilty. Johnson scolds Aiken for his bias, saying everyone deserves a proper defense.
Baker and Hamilton attend the trial. To his shock, Aiken's wife attends as well. He asks her why she is here. Sarah says she is trying to see why he is here defending Mary Surrat.
The accused are led out to the pews and the charges are read out. The tribunal led by David Hunter (Colm Meaney) asks how Mary pleads. Mary says she is innocent. The other conspirators have plead not guilty as well. Hunter moves for opening statements but Johnson stands up and asks for a continuance. Hunter scoffs at the request, saying a delay would put the public through more pain. Johnson says that the government had a month to prepare its case while Mrs. Surrat was only to meet consul yesterday. Hunter denies the request.
Having no choice, Johnson makes his opening statement. He says that a military tribunal of a civilian its the worst possible action they could of partaken. The Constitution was made for this very type of situation; so civil rights could not be suppressed in times of emotional instability.
Johnson talks to Aiken, saying he will have to stand down. Surrat is already guilty in the eyes of the nation, and having a Southerner defend her will just make it worse. He wants Aiken, a former Union solider to do the job. Aiken doesn't want to do it because he thinks she is just as guilty as everyone else, but Johnson tells Aiken to do his job and defend a client.
Aiken goes to the fort where Surrat and the conspirators are being held for trial. A solider stands by despite Aiken's claim for privilege. Aiken asks for information about herself because he only knows what he reads in the papers and it is very unflattering. Surrat tells him she moved to DC the year before after her husband died and opened up a boarding house to make money. She knew the men as tenants and nothing more, she knew little of what was going on. They were confidants of her son John. Her daughter Anna was deliberately kept out of the loop from what was happening by her.
Aiken is not impressed with the info, saying she must of know what John was up to with Booth and the other conspirators. He makes it clear that this is a military trial, her judges are generals, and she cannot testify in her own defense. She will most likely hang if found guilty. Surrat does not want to give up more information, so Aiken leaves with not much to go on.
Aiken goes to see Anna Surrat (Evan Rachel Wood) daughter of Mary. Aiken presses for information about John but Anna doesn't want to have her brother crucified. Aiken makes it clear that her mother will pay the price instead. He learns a little about the meetings and how she was always told to go away by her mother when they were about to occur. One of the tenants Louis Weichmann (Jonathan Groff), was loved by Mrs. Surrat like a son. Aiken goes to John's room and finds a ticket stub to Richmond with Weichmann's signature on it. A rock slams through the window by an unknown assailant. Aiken asks the solider standing guard if he saw what happened to which the man denies seeing anything (or rather didn't care).
At trial, Weichmann is the first witness for the prosecution. He tells the court he knew Booth, John Surrat and others were meeting in Mary Surrat's boardinghouse and that she knew about what they were planning. Surrat loses her cool and calls him a liar and told to be quiet. During cross examination, Aiken questions Weichmann's knowledge of the meetings since he never actually attended any of them. Aiken asks if Weichmann has been to Richmond which he initially denies. When confronted with the ticket, he backpedals saying he was planning on going to school up there. Aiken thinks otherwise, saying Weichmann could of been contacting rebels up there, for Booth and others. The tribunal warns Aiken that Weichmann is not on trial and tells him to watch himself. Weichmann is excused.
Aiken has another jailhouse visit with Surrat who is meeting with a priest. The priest says Mary is not eating and perhaps he could convince her to. Aiken tells her that he doesn't have much faith in the case and asks if she knows where John was. They have to focus the trail on him, not her. Surrat denies knowing where her son his and saying he was out of town when the assassination happened and he is not a killer. Aiken gets up to leave again when Surrat says John wasn't planning on killing Lincoln...they were going to kidnap him.
Aiken listens to the whole plot. John, Booth and a few others were going to ambush the carriage carrying Lincoln and hold him ransom for all the Confederate soldiers in jail. On the eve of the plan, they find out that Lincoln changed his plans and would not be coming. So the kidnapping plot turned into an assassination. Aiken leaves to build more of his case.
Aiken goes to see Anna Surrat and she turns over the boardinghouse ledger.
The prosecution calls its second witness, a Major Smith (Chris Bauer). Smith was the lead solider on the raid of the Surrat's boardinghouse. There they found a picture of John Wilkes Booth hidden behind one of Anna's photos, insinuating that Anna Surrat was infatuated with him and knew more, and thus Mary Surrat knew more. Lewis Payne came to the house, posing as a gully digger. When pressed to identify him Mary Surrat denied knowing him, making it seem as if she was covering for him. Aiken challenges that claim saying Lewis Payne was living under a false name, bringing the ledger into evidence. Furthermore, it was dark and he has a sworn statement from a doctor that her eyesight is bad. Aiken asked if it was possible that Mary Surrat just could not see him, which Major Smith says it is possible, giving reasonable doubt.
Aiken spends time with friends Baker and Hamilton. They along with Sarah question why he would defend Mary Surrat as her side tried to kill him during the war. Aiken doesn't have a good answer for them.
Mary is still not eating and is living on poor conditions. Her health is getting worse. Aiken talks to an aide of Stanton, arranging it so that Surrat gets a day of fresh air and better food under the pretense of keeping the trial going without a hitch. Aiken and Surrat talk and Surrat asks if Aiken ever fought for something bigger than himself. Being a veteran, Aiken is insulted by the comment. Surrat makes the most of her time outside, taking a walk around the grounds.
The prosecution calls their final witness. The man, John Lloyd (Stephen Root) testifies that Mary Surrat came by the day before the assassination with Louis Weichmann to deliver a package from John Wilkes Booth. Furthermore, she asks him to get guns and whisky. Surrat yells he is a liar and has to be quieted again. Lloyd continues saying that two men, one of them being Booth came by for the guns and whisky later after Lincoln was killed. Aiken asks if anyone saw this conversation and Lloyd said Surrat pulled him aside. Aiken says that is convenient. Aiken says he has proof that Lloyd is a drunk himself so his credibility is bit off. He waited several days to tell investigators this information not out of fear, but because it would look like he was part of the conspiracy. Furthermore, Lloyd admitted that John Surrat forced him to help hide weapons not Mary Surrat. John is the guilty one, not her. Surrat then yells at Aiken to stop, for she didn't want her son to be spoken ill of. Lloyd is excused and the prosecution rests its case.
Aiken calls a Union solider that supposedly heard no statements regarding Surrat. However on the stand the man lies, saying he heard certain statements that incriminate Mary Surrat and her son. Aiken has to excuse the witness. He challenges the prosecutor in open court saying they made the rules, they picked the judges, and now they have tainted all his witnesses by secretly threatening all of them with jail time or worse. Hunter warns Aiken that if he continues he could be in contempt of court.
That night, Aiken and Sarah go to The Century Club for a soldiers celebration. At the door they find out Aiken has been blacklisted from the club for his defense of Mary Surrat. Sarah is aghast and wants to go home. Aiken tries to talk to her but she tells him he shouldn't risk everything for Mary Surrat. Aiken sees Stanton and tells Sarah to wait. He confronts Stanton calling the trial an abomination. He and Stanton have a few tense words and Stanton go inside, but not before he would settle for Mary Surrat if they cannot have John. When he looks back, Aiken sees his wife left in the carriage without him. He goes to a bar and gets drunk.
Aiken sees Anna Surrat and says she will have to testify. Anna says she will say her mother is innocent. Aiken says she will have to say her brother was not. Anna tells Aiken about the last night she saw her brother. He was leaving, claiming to go speculate cotton prices. Her mother begged him not to go, thinking he was going to get himself killed but John pushed her down saying his fight was worth something.
On the stand, Anna is shielded from her mother by soldiers and she tells her side. She knew about the meetings but never heard anything. She had that picture of Booth because she had a crush on him. Her brother saw it and told her to destroy it, "as that man will destroy our family." Aiken uses that statement to confirm that John knew what Booth was planning and that John was taking steps to safeguard from prosecutions for his crimes. Anna says yes. Mary screams for her daughter to be quiet and has to be hushed again. Anna Surrat is excused and cleared from any prosecution in the case. Anna is denied access to her mother and Aiken convinces the tribunal to show a small bit of compassion by allowing a child to see her mother.
Aiken goes to see the family priest that Mary Surrat saw in prison. Aiken demands to know where John Surrat is. The priest claims he does not know and can only pass on a message. "Tell John Surrat that his mother is going to pay for HIS crimes." Aiken leaves disgusted.
Aiken has no more witnesses to call and has only one more shot; his closing statement. Aiken tells the court that a military tribunal of civilians was the wrong choice to make. Mary Surrat is only on trial for three reasons; because she knew Booth, because they planned in her house, and that her son John was one of the conspirators. Any of these alone are not enough to convict and even together are a faulty premise at best. The state's witnesses moral character is in question, and possibly they incriminated Mary Surrat to place blame away from themselves. Aiken urges caution and rational thinking in the matter. "DO NOT let this injustice occur due to revenge." Aiken warns the tribunal.
The tribunal deliberates. They agree that Lewis Payne and two other men will be hanged. But when they get to Mary Surrat they cannot get to a decision.
Stanton is furious by this. He wants them convicted, executed, and forgotten. He says they will persuade the tribunal to vote HIS way.
Mary Surrat is told of the verdict. She is guilty on all three counts. She is to hang with the other three men. Anna is delivered the news and is crushed. John Surrat also receives the news and remains stoic.
Aiken talks to Mary Surrat and tries to comfort her. Surrat blames herself because she sheltered her son so much so he wouldn't be like his father. "And this is what he chose to do." Surrat says bitterly.
Aiken talks to Johnson who tells him there are only three options. He could petition President Andrew Johnson for clemency which he will not grant. He could find a judge to argue for a new trial but no one will want to do that either. Or John Surrat could give himself up before his mother is hanged tomorrow. Aiken decides to write a writ for Habeas Corpus.
Burning the midnight oil, with Baker and Hamiliton at his side, Aiken writes a brief for a new trial and presents it to Judge Wiley who was hand picked by Lincoln himself. Despite Wiley's reservations, Aiken convinces him that Lincoln would not want this to happen; that rights need to be protected AT ALL times. Judge Wiley signs the document.
Aiken delivers the writ to Stanton saying Mary Surrat is to be transferred to court at noon. Aiken delivers the news to Mary and Anna and they are overjoyed at a chance for her to be set free. Aiken looks to the gallows and sees four nooses. There should only be three...
Soldiers come and tell Mary Surrat it is time. Aiken says he has a court order to transfer her, but a solider shows a letter from President Johnson. A spiteful Stanton appealed to the President who then rejected the appeal. Anna begs Aiken to do something but he cannot. Every avenue has been exhausted. Mary Surrat is taken to the gallows while Anna has to be restrained by Aiken.
Mary goes to the gallows and is hanged with the three men. Aiken watches in horror, now fully in belief in her innocence and the injustice of her death.
16 MONTHS LATER
Aiken returns to the jail where Mary Surrat's son John is. He was captured and now awaits trial. Aiken says he cannot help since he left the law a while back. He presents Mary's rosary beads and tries to give them to John. John says to keep them for himself. "You were more of a son to her than I ever was." John says, ashamed that his actions indirectly killed his mother. Aiken leaves the jail.
Title cards inform us that a year after Mary Surrat was tried and executed, The Supreme Court unanimously declared that civilians must be tried in a court with a jury of their peers regardless of the crime.
Her son, John Surrat was tried under that new rule. A jury of Northerners and Southerners could not come to a decision regarding his guilt and in an ironic twist, he was set free and lived out the rest of his life.
After he left the law Frederick Aiken became the first City Editor of The Washington Post.
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